1. Field of the Invention
This invention relates to a method of bonding a room temperature vulcanizable silicone ;sealant to a porous substrate.
2. Background Information
The use of silicone sealants to bond to porous substrates such as concrete, marble, brick, and stone is a problem for the construction industry. The use of a neutral silicone sealant for such purposes is highly desirable because such sealants have little or no deleterious effects on the porous substrates against which they are cured. However, when such sealants are used, especially those which contain silicon-bonded alkoxy and titanate curing catalyst, bubbles form in the sealant during the curing process when the substrate is hot, such as when the sun heats the building materials to temperatures exceeding 40.degree. C. Such bubbles are unacceptable and can increase the volume of the cured product by as much as two or three times compared to the cured product not cured on a hot porous substrate. The reason these bubbles form during cure of this kind of sealant composition on surfaces of hot porous substrates has not been specifically determined, but it is believed that substrates react with the curing sealant composition releasing alcohols which vaporize and which are trapped by the rapidly curing sealant composition to produce the bubbles. The inventors realize that there may be other explanations for the bubble phenomenon and do not wish to be held to this specific theory. The following solution to this bubbling problem is the object of the present invention.